The present invention relates to the field of marine seismic exploration. Specifically, the invention is concerned with a method and apparatus for determining the positions of seismic subarrays in relation to one or more towed marine seismic streamer.
Marine seismic exploration is usually conducted by towing one or more submerged seismic streamers through the ocean. The streamers are provided with a plurality of pressure sensors, such as hydrophones, disposed at appropriate intervals along the length thereof. One or more seismic energy source, each comprising one or more subarrays, utilize air guns to propagate pressure waves through water in the vicinity of the marine streamer and into the underlying seafloor. The pressure waves radiate in all directions, and some waves travel downwardly through the earth, a portion of the waves being reflected upwardly at levels where there is a contrast in the acoustic impedance characteristics of the strata. This is subsequently detected by the hydrophones as pressure variations in the surrounding water. These pressure variations are transformed into electrical signals by the hydrophones and transmitted via the streamer to recording apparatus onboard the tow vessel where the collected data can be interpreted to reveal information about the subsea geological formations.
It is necessary, for the signals to be meaningful, to know the location not only of the individual hydrophones with relation to the tow vessel, as disclosed in U.S. Pat. No. 4,376,301 which is incorporated hereinto, but also the position of the air gun and subarrays with respect to the streamer, such guns being preferably suspended below floats of seismic subarrays on either side of the marine streamer. Inasmuch as the tow vessel is continually moving, and since the location of the seismic subarrays and the streamer can potentially vary in relation to each other, ascertainment of the relative locations of the floats to the streamer is difficult.
As above mentioned, the prior art has developed various systems in order to ascertain the location of the marine streamer, but the prior art is remiss in providing a method for locating the seismic subarray with respect to the streamer. Accordingly, the present invention is directed to overcoming this problem in the art.